Form FEMA Form 086-0-27 FEMA Form 086-0-27 Alluvial Fan Flooding Form

DEPARTMENT OF HOMELAND SECURITY

Federal Emergency Management Agency
ALLUVIAL FAN FLOODING FORM (FORM 6)

OMB Control Number: 1660-0016
Expiration: 4/30/2017

PAPERWORK BURDEN DISCLOSURE NOTICE
Public reporting burden for this form is estimated to average 1 hour per response. The burden estimate includes the time for reviewing
instructions, searching existing data sources, gathering and maintaining the needed data, and completing, reviewing, and submitting the form.
You are not required to respond to this collection of information unless it displays a valid OMB control number. Send comments regarding the
accuracy of the burden estimate and any suggestions for reducing this burden to: Information Collections Management, Department of
Homeland Security, Federal Emergency Management Agency, 500 C Street, SW, Washington, DC 20472 , Paperwork Reduction Project
(1660-0016). Submission of the form is required to obtain or retain benefits under the National Flood Insurance Program. Please do not send
your completed survey to the above address.
PRIVACY ACT STATEMENT
AUTHORITY: The National Flood Insurance Act of 1968, Public Law 90-448, as amended by the Flood Disaster Protection Act of 1973, Public
Law 93-234.
PRINCIPAL PURPOSE(S): This information is being collected for the purpose of determining an applicant's eligibility to request changes to
National Flood Insurance Program (NFIP) Flood Insurance Rate Maps (FIRM).
ROUTINE USE(S): The information on this form may be disclosed as generally permitted under 5 U.S.C § 552a(b) of the Privacy Act of 1974,
as amended. This includes using this information as necessary and authorized by the routine uses published in DHS/FEMA/NFIP/LOMA-1
National Flood Insurance Program (NFIP); Letter of Map Amendment (LOMA) February 15, 2006, 71 FR 7990.
DISCLOSURE: The disclosure of information on this form is voluntary; however, failure to provide the information requested may delay or
prevent FEMA from processing a determination regarding a requested change to a (NFIP) Flood Insurance Rate Maps (FIRM).
Flooding Source:
Note: Fill out one form for each flooding source studied
A. THREE STAGE ANALYSIS (Based on DHS-FEMA Guidelines dated February 23, 2000)
1.

Stage 1 Analysis
a. The landform is composed of alluvium derived primarily from (check one)

Fluvial

Debris flow

Combination deposits

b. Source(s) of data used to determine composition, morphology, and location of the landform:

DRAFT
Yes

c. Is there an NRCS soils survey and soil survey map available?

No

If Yes, please include a copy of the map and any pertinent sections of the soil survey.
d. Is there geologic mapping available?

Yes

No

If Yes, please include a copy of the map and any pertinent geologic map unit descriptions.
e. Is there historic aerial photography available?

Yes

No

If Yes, please include any copies of the site-specific photography.
2.

Stage 2 Analysis
a. The alluvial fan landform exhibits

Active

Inactive

A combination of active and inactive alluvial fan flooding

b. Approximate age of inactive fan surfaces (thousand of years):

yrs. Source of age estimate:

c. Is there an opportunity for avulsions that could lead to channelized or sheet flooding across the older fan surfaces?
Yes

No
(

Basis:

Hydraulic modeling

Geographic analysis

d. Is there geomorphic evidence of past avulsions during Holocene epoch?
e. Approximate age of past avulsions:

Other (describe)
Yes

No

yrs. Source of avulsion age estimate:

f. The active portion of the alluvial fan landform exhibits the following types of flooding (check one):
Flooding along stable alluvial channels
Sheet Flooding
Debris Flow
Unstable flow path flooding

FEMA FORM 086-0-27B (06/17)

Page 1 of 3

A. THREE STAGE ANALYSIS (Based on DHS-FEMA Guidelines dated February 23, 2000) (continued)
g. The active portion of the alluvial fan landform exhibits the following types of flood processes (check one):
Recently active sediment deposition
Recently active channel or floodplain erosion
Recent channel avulsions
High velocity flood flows
Shallow sheet flooding
h. Methods used to support Stage 2 Analysis (check all that apply):
Geomorphic analysis
Field studies
Historical evidence
Hydraulic modeling
3.

Stage 3 Analysis
The boundaries of the 1%-annual-chance floodplain have been determined using (check all that apply):
Risk-Based Analysis
FEMA FAN Program (if discharge at the apex is different than that given in the effective FIS, then attach MT-2, Form 2 along
with a plot of the flood frequency curve on log-normal probability paper and include the drainage area above the hydrographic
apex, and the mean, standard deviation, and skew coefficient of the Pearson Type III frequency curve)
List basis for avulsion coefficient used:
FAN used in

Single

Sheet Flooding Methods

DRAFT
Multiple channel mode

Hydraulic Analytical Methods
List models & versions used:

Geomorphic Data, Post-Flood Hazard Verification, and Historical Information
Composite Methods (indicate which methods by checking above)
The active alluvial fan area has the following characteristics:
Highly active
Conical shape
Unstable flow paths
Entrench stable channel networks
Constructed channels
Debris flow flooding
Undulating terrain

Urbanization (homes, roads, embankments, levees, railroads, canals, etc. that would after natural flow conditions)
Flooding sources evaluated:
Flow from watershed above hydrographic apex
Method:
Flow from rainfall on fan surface
Method:
Flow from tributaries joining active fan area below hydrographic apex
Method:
FEMA FORM 086-0-27B (06/17)

Page 2 of 3

B. STRUCTURAL FLOOD CONTROL MEASURES
1.

The following structural flood control measures are proposed or built (check all that apply):
Channelization

Levee/Floodwall

Dam

Sedimentation Basin

Other

2.

Do the constructed or proposed structural measures affect flood hazards (including velocity,
scour, and sediment deposition) on other areas of the fan?:

3.

Attach completed Form 3 (Riverine Structures Form) for each structure.

4.

Sediment Transport Considerations:
Was sediment transport considered?

Yes

Yes

No

No

If Yes, then fill out Form 3, Section F (Sediment Transport). If No, then attach your explanation for why sediment
transport was not considered.
5.

Please attach a copy of the formal Operations and Maintenance Plan.
C. MAPPING REQUIREMENTS

Attach a certified topographic work map showing the following:
The boundaries of the alluvial fan landform including: toe, topographic and hydrologic apexes, and lateral boundaries
The delineation of the active and inactive portions of the alluvial fan landform as determined by the Stage 2 analysis
The revised 1%-annual-chance floodplain boundaries, as determined by the Stage 3 Analysis, that tie into the effective
floodplain boundaries. Indicate where each delineation methodology used was applied if more than one methodology was
used
The correct alignment of all structural features

DRAFT

The map scale and a north arrow

FEMA FORM 086-0-27B (06/17)

Page 3 of 3